The Universal Mobile Telecommunications System (UMTS) represents one of a number of mobile radio systems which provide the subscriber of a mobile terminal with a large number of services.
UMTS operates in the bands from 1885 to 2025 MHz and 2110 to 2200 MHz, and also allows data rates of up to 2 Mbit/s by means of the already known functionality of narrowband mobile radio systems.
One aim of the UMTS mobile radio system is to provide a standard third-generation mobile radio system for subscribers throughout the world, and for the first time to allow roaming and handovers between technically different networks, such as GSM (Global System for Mobile Communications) using dual-band and dual-mode terminals.
Owing to the selection of different codec modes for a subscriber A and a subscriber B or in the event of an interruption with TrFO (Transcoder Free Operation), communications networks which are based on the UMTS Standard require the capability to transcode in the UMTS mobile switching centers (UMSC) existing connections from an AMR (Adaptive Multi Rate) codec mode to a different AMR codec mode. A call from a subscriber is transmitted in a compressed form, for example by means of an AMR codec in the case of UMTS, via a speech channel of an air interface in a mobile radio network. An AMR codec contains an algorithm that is specific for it and which compresses speech data. An RNC (Radio Network Controller) in a mobile radio network negotiates a set of AMR modes with a switching center via which the speech connection is intended to be set up before a UMTS speech connection is set up. The switching center has to be able to intervene in the connection in order to make it possible to feed further information into the connection or into the call. In this case as well, it is accordingly necessary to once again code existing connections from an AMR codec mode onto the same AMR codec mode or onto a different AMR codec mode, for example in order to feed in tones based on TDM.
Transcoding such as this is conventionally carried out by decoding data that is transmitted using a first codec mode into 160 linear samples of 13 bits, and by subsequent encoding into a second codec mode. For this purpose, data which has been transmitted to the switching center within a data frame that is transmitted from a radio network UTRAN with a separation of 20 milliseconds is decoded by means of a decoding device, with the data previously having been coded using a first AMR (Adaptive Multi Rate) codec mode. If, for example, this is speech data, then the speech data contained in the speech frame is converted, after it has been decoded, into linear pulse-code-modulated (PCM) words with a length of, for example, 13 bits. These are then compressed using a so-called A/μ law to form words with an information content of 8 bits, and are time-division multiplexed via the time-division multiplexing switching matrix. The time-division multiplexed data is decompressed to form linear pulse-code-modulated words with an information content of, for example, 13 bits, and is then coded in a new AMR codex mode.
Owing to the use of the synchronously operating TDM switching matrix, coding and decoding are required for the insertion of tones and/or announcements, and this necessitates additional coding and decoding system units.
Various UMTS Standard versions may be used within a connection, depending on the various network sections within the communications network, which is based on the UMTS Standard.